Indian Defence Review

The Event

On 21 Sep 2021, a small drone was destroyed using the L-70 gun, duly integrated with an Anti-Drone System (ADS). This integration was demonstrated by Zen Technologies limited; a Hyderabad based company with a lead and a commanding presence in the design, development and manufacture of state-of-the-art combat training solutions for defence and security forces worldwide.

The event passed quietly, probably not the ‘Breaking news’ material.  This article brings out how this little event is of much significance as marks the acquisition of a new capability on the indigenous route.

THE UNMANNED THREAT SPECTRUM…

Ever since the advent of the unmanned phenomenon, the battlefield has never been the same. That said, over a period of years and decades, the Unmanned Aerial Systems ( UAS) have grown into five type of threat verticals. Just to take their names:-

1. UAS as reconnaissance threat vehicles. More appropriately the UAS being used for intelligence (gathering), surveillance, target acquisition and reconnaissance (ISTAR) role in the battlefield.
2. ISTAR vehicles modified to carry weapon loads (intrinsic or strap- on) for precision strike on a variety of targets in the Tactical Battle Area (TBA).
3. Dedicated strike UAS armed to the teeth with guided rockets, missiles and hard and soft-kill precision/loiter munitions for independent strike missions in the battlefield.
4. Dedicated UAS operating in joint missions with combat platforms. Such missions produce disproportionate effects by combining the strengths of ‘man and machine’ in operations that go by the name of Manned and Unmanned Teaming or MUMT.
5. Small drones either operating in small numbers or in large groups (called drone swarms) capable of causing a variety of damage and destruction on the adversary (explained later).

Drone swarms are amazing kill vehicles. These possess the intelligence of a locust swarm. Powered by the tools of AI, a swarm body displays ‘collective intelligence’ and is capable of taking decisions with a high tolerance for ambiguity and can conduct ‘intelligent autonomous warfare’.

It is stated that while the conventional air defence means consisting of ‘sensors’ (to detect the UAS electronically at long ranges), ‘shooters’ (to kill the UAS once detected and tracked) and the battle management command and control  (BMC2) systems (which digitally control the air defence battle, all of a few minutes and seconds) are sufficient to tackle the UAS described at serials1-4 above, small drones at serial 5 are a big issue.

WHY SMALL DRONES ARE A BIG ISSUE?

Before attempting an answer to this poser, it is essential to see what exactly is small drone?

Small Drone – the little monster.[1]^,[2],[3]

A small drone is a low-cost (mostly DIY variety) UAS. It is normally 7-8 ft in length, 6-7 ft in breadth and weighing around 15-20 kg. It can normally carry a warhead of 5-10 kg. It has either a four/six rotor configuration (quad/hexacopter) or a small fixed wing construction.

A small UAS basically has three features, namely, a communication and a navigation device based on GPS, battery for powering the rotors and a payload with varying options of dropping/firing etc. The warhead range could include explosives, IEDs, small arms, ammunition or tailor- made load packages etc.

These are the type of drones that are regularly seen in our border areas carrying out a variety of dropping/firing activities. It will be recalled that a similar drone attack that took place on the Air Force station Jammu on the night of 26/27 Jun created a national uproar.

What are the challenges in killing small drones?

Killing of small drones as described above poses two challenges:-

1. Challenge 1: Detection Challenge.

Due to their miniscule configuration, small drones have a very low ‘degree of detectability’ by conventional radars. This degree of detectability is called radar cross-section or RCS. Higher the RCS, higher will be the range and altitude at which the body will be detected by an  electronic surveillance device such as radar.( technical details not explained).

A typical RCS of a UAS measured in m² may be just 0.3- 0.5 compared to a combat aircraft whose RCS is many magnitudes more (SU 30 MKI 4m², Mig 21 – 3 m², F16 C – 1.2m^2 [4]. Stealthy aircrafts however have much lower RCS ( F -35 – .005 m2, J 10 -0.5-1.5m², J 20 – 1-3 m²– design flaw)[5].

2. Cost of Kill Challenge.

To sustain an air-attack-air defence duel, the cost of kill on both sides need to balance. If one side starts inflicting asymmetric costs on the other, the latter will loose in the long run. This logic applies when millions of dollars missiles are launched to kill UAS costing not more than a few hundred dollars.

If such a thing happens The attacker has already won. Low cost UAS require low cost kill options. This is the reason why Israel’s Iron Dome will fall short in the long run.[6]

HOW THE ABOVE CHALLENGES ARE RESOLVED?

Stated in nutshell, the above two challenges are resolved as under:-

1. Resolving Detection Challenge.

By employing such radars which have been specially designed for detecting small RCS targets. These could be Active Electronically Scanned Array (AESA) Radars or radars in frequency bands of 6-15 GHZ (called C, X, Ku and Ka bands) which are found to be effective in detecting small targets. Another variety of radar called the Frequency Modulated Continuous Wave (FMCW) radars is also a good small-target detector. (details not explained).

By employing Electro-Optical (EO) surveillance devices which are most ideal to detect small drones. A full detect-kill package is called Electro Optical Fire Control System (EOFCS). A typical EOFCS has a day camera, a thermal (night) camera (based on forward looking infra-red or FLIR), an RF detector, a Laser Range Finder (LRF), a Fire Control Computing Device (FCCD) and, a Video Display Unit (VDU).

Small drones operating in visual domain, are detected either by day/night cameras while the target range is assessed by the LRF. The FCCD calculates the future impact point of the target. Once this data is available, the associated kill means destroy/ disable the drone.  Al that an operator has to do is to keep the target on the cross-wires in the VDU.

By employing acoustic sensors to detect the typical buzz of small drones in the visual range. Though these sensors are effective but the same can get badly degraded due to battlefield noises.

2. Resolving the kill challenge.

Low-cost kill options include the following:-

1. Killing the small drones in visual domain by employing small arms (SAs) in direct firing role (100-500/700m range).
2. Enhancing the power of SAs by strapping on EO sights on them. This makes them capable of detecting small drones at longer ranges.
3. Employing RF/EW jammers to disable/cripple the electronics and (or) communication links on board the drones so as to achieve the following:-
4. Cutting the navigation links between the drone and the GPS thus making the drone rudderless.
5. Cutting the communication link between the drone and its Ground Control Station (GCS) thus severing its umbilical chord of command and control.Taking control of the drone through hacking/phishing attacks which can then be steered to land/crash harmlessly.
6. Using lasers to ‘fry’ (burn off)/ cripple/disable the electronics and electro-magnetics on board the drone to kill it.

3. Sub-optimality in above kill solutions

Following sub-optimality exists in above kill challenges:-

1. SAs are effective only in their very finite range. The fire is direct and does not cater for the move of the drone during the time of flight of the round (however small) thus adding to inaccuracy.
2. Normally on being killed by RF/EW/laser etc., the drone is programmed to initiate a default command of ‘return to base’ .This spares the drone to fight another day.
3. The above kill options will only be partly effective in dealing with drone smarms, firstly because of their large numbers and secondly, due to their inbuilt survivability capability.

4. The kinetic kill

Kinetic kill option unfolds as under:-

1. The drone is detected using suitable small RCS capable radar and/or an EO surveillance device.
2. Based on the present position of the target, as determined by day/night camera/RF detector etc. and with the range as given by the LRF, the FCCD gives out the future position ( likely impact point)  of the target.
3. A high rate and volume of fire (2000-8000 rounds/min or rpm) gun is made to fire on the future position of the target as calculated.
4. The warhead ensures a much higher kill effect in its applicable zone-of-effectiveness. If the fuse has proximity kill feature (exploding the warhead in the set vicinity of the target, even without impact) the kill effect is increased.

5. Virtues of Kinetic kill

1. Fire is at predicted future position of the target hence much more effective ( future position – a position where a moving target will go to from its present position during the time, the gun projectile travels from the gun and reaches to it)
2. High rate and volume of gun fire increases cumulative kill probability (CKP).
3. Proximity fuse feature (if present) considerably increases the volume of kill zone.
4. Will be comparatively more effective on a drone swarm than other kill options.
5. Low-cost high-effect kill for small drone targets.
6. Drones not spared to fight another day.

APPLYING THE KINETIC KILL SOLUTION ON L-70 GUN

1. Some factual details

1. L-70 is a towed air defence gun , the first version of which (L-60 gun) was produced by M/s AB Bofors Sweden in 1947[7].
2. The induction of these guns in India started in 1964. A large number of these guns are currently held by the field force. (quantum classified).
3. Despite its vintage, the gun is still operationally relevant today.
4. A certain number (classified) of these guns have been upgraded. The upgrade package includes the following:-

1. A fully packaged EOFCS as described above.
2. Much faster response through electrical drives. (earlier hydraulic drives)
3. On board power supply for autonomous operation.

The Fire of L-70 gun is controlled by a Fire Control Radar (FCR) which tracks the target and predicts its future position. The radar data is passed to the gun to fire at the predicted future position. The current FCR with the gun is the I/J/K Band Flycatcher radar (country of origin Netherlands, later made/upgraded in India under licence).

Brief technical characteristics of L-70

1. Range                 –  3500m
2. Rate of fire          –  300 rpm
3. FCR search range –  20km
4. Weight of round    –  2.5 kg
5. Weight of warhead – 0.102 kg

2. Integration of ADS with L-70

Since the FCR associated with the L-70 gun (Flycatcher radar) is unable to detect small drone targets, an ADS, as explained above, has been integrated with the gun. As stated, this ADS has been designed by Zen Technologies Limited and is called Zen ADS.

Some relevant points about the Zen ADS are enumerated:-

1. The ADS detects the small drone using a dual-mode surveillance and tracking capability based on Electro-Optics surveillance, as well as, by an RF based surveillance.
2. A combination of both these detection solutions ensures that a low RCS drone, which would otherwise be invisible to conventional radar (such as Flycatcher), becomes detectable.
3. The detector has a capability to detect up to 100 drones at one time with a response time of <0.1 sec. This makes the detector particularly useful for swarm drone detection.
4. The three mode RF detector covers very wide frequency range (92 MHz – 6 GHz) and bandwidth of 25 MHZ extendable to 40 MHZ. Such a wide frequency range and bandwidth ensures that every tone and tenor of small drones is likely to be detected.

In addition to the RF based detection, there is also a Video based Drone Identification & Tracking (VDIT) unit which features both the day as well as night camera sensors. VDIT is capable of capturing and tracking video up to a range of 3 Km.

1. The above EO surveillance and tracking is aided by an X band 2D/3D AESA radar which detects the drones as per the radar detection range specifications and provides precise data for target coordinates both in azimuth and elevation.
2. All the above data is fed to the Data Fusion and Command Centre (DFCC) associated with the ADS which calculates the future position of the target ( likely impact point)  based on the time of flight of the L-70 projectile.
3. This data in terms of future gun bearing and elevation is fed to the  L-70 gun which fires at the future position of the target.
4. The drone is destroyed by the L-70 warhead in its zone of effectiveness.

UNDERSTANDING WHAT HAS BEEN ACHIEVED

In this context, following points are stated :-

1. It has been possible to make available a fully indigenous kinetic kill solution for small-drone/swarm drone killing.
2. It has been possible to overcome the limitation of the existing  FCR of  L-70 gun (Flycatcher radar) in detection of  small RCS drones by innovatively integrating an EO surveillance and tracking system with it.
3. By accurately replicating the data-bus algorithm chain of Flycatcher radar to L-70 gun, it has been made possible to feed the future position data of the target to the gun not from the radar but from the ADS itself Due to the  similarity of data bus, the gun perceives the ADS data  as if it is coming from the radar and produces the kill effect of predicted fire.
4. The target is killed the substantial L-70 round warhead in its zone-of effectiveness..
5. The association of X Band AESA radar along with EO systems doubly ensures that small drone positively gets detected notwithstanding its small RCS.
6. Large number of vintage L-70 guns find a new relevance in the anti-drone role giving all the virtues of kinetic catastrophic kill as explained above.
7. Zen Technologied Limited, deserve due credit in bringing out this 100% indigenous and innovative integration of EO based dual-mode surveillance with a kinetic kill solution.

The skillful integration of ADS with the L-70-Flycather data-bus algorithm is indeed a win-win as it picks up the best option both in small RCS surveillance and tracking, as well as, the accuracy of kinetic kill with predicted fire.

The premise that the event that passed off rather quietly on the sea-coast at Army Air Defence College on 21 Sep21 was indeed a big achievement, stands corroborated.

Courtesy: https://www.claws.in/an-important-milestone-achieved-quietly/